1. Field of the Invention
The invention relates to an exhaust gas purification apparatus and an exhaust purification method for internal combustion engines.
2. Description of the Related Art
Internal combustion engines include a movable component that is operated during the engine operation and the operation of which causes the temperature of exhaust gas to change, such as an EGR valve, a variable nozzle of a variable-capacity turbocharger, an intake throttle valve, and an exhaust throttle valve (For example, refer to claim 5 and Para. 0021 of Japanese Patent Application Publication No. 2005-48701 (JP-A-2005-48701)).
Some of such internal combustion engines are provided with an exhaust gas purification apparatus that executes an exhaust gas temperature increasing control for increasing the exhaust gas temperature during a recovery process for recovering the exhaust gas purification capacity of an exhaust gas purification device, and it is possible to increase the exhaust gas temperature through the operation of the foregoing movable component during the exhaust gas temperature increasing control. For example, Japanese Patent Application Publication No. 2005-48701 describes increasing the exhaust gas temperature by controlling the opening degree of at least one of an intake throttle valve, an EGR valve, and a variable nozzle of a variable-capacity turbocharger. Further, Japanese Patent Application Publication No. 2005-48701 describes increasing the exhaust gas temperature by retarding the fuel injection time without using the movable component.
With regard to the exhaust gas temperature increasing control, in view of increasing the exhaust gas temperature effectively, it is not the best way to increase the exhaust gas temperature through the operation of the movable component (e.g., by opening the EGR valve) in the entire engine operation region. That is, the exhaust gas temperature can be effectively increased by opening the EGR valve only in a limited engine operation region. In other words, the exhaust gas temperature can not be effectively increased by opening the EGR valve in the other engine operation regions. Therefore, in order to increase the exhaust gas temperature effectively, it is preferable that the exhaust gas temperature be increased by opening the EGR valve in the aforementioned limited region and the exhaust gas temperature be increased without using the EGR valve in the other engine operation regions.
Meanwhile, there is a possibility that the EGR valve be temporarily stuck up at the full-close poison by, for example, being frozen when the internal combustion engine is off in a low temperature. In this case, the EGR valve can not be utilized to increase the exhaust gas temperature in the exhaust gas increasing control, and therefore the recovery process for recovering the exhaust gas purification capacity of the exhaust gas purification device can not be properly performed, and the purification of the exhaust gas of the internal combustion may become insufficient.
Note that this problem occurs not only in the case where the EGR valve is used as the movable component utilized to increase the exhaust gas temperature but also in the case where an intake throttle valve, an exhaust throttle valve, a variable nozzle of a variable-capacity turbocharger, or other movable component is used as the movable component utilized to increase the exhaust gas temperature.